Compressionally-loaded spring forming a dc connection to the conductor of an rf transmission line



3,521,202 COMPRESSIONALLY-LOADED SPRING FORMING A DC CONNECTION T. J. RUSSELL July 21, 1970 TO THECONDUCTOR OF AN RF TRANSMISSION LINE Filed Dec. 4. 1968 IINVENTOR. THOMAS J. RUSSELL ATTORNEY us. Cl. 333-91 United States Patent 3,521,202 COMPRESSIONALLY-LOADED SPRING FORMING A..DC CONNECTION TO THE CONDUCTOR OF AN RFTRANSMISSION LINE Thomas J. Russell, Sunnyvale, Calif., assignor, by mesne assignments, to The Singer Company, New York, N.Y., a corporation of New Jersey Continuation-impart of application Ser. No. 598,510, Dec. 1, 1966. This application Dec. 4, 1968, Ser. No. 781,211

Int. Cl. H01p 1/00 I 6 Claims ABSTRACT THE DISCLOSURE An electrical connection formed by a conductive, helical coil compression spring to at least one of the two spaced apart conductors of an RF transmission line and across the space between the conductors in which the axial integrity of the spring along its length is maintained by an internal core or external sleeve.

This invention relates to direct current (DC) conductive connections to at least one of the spaced apart conductors-of a radio frequency (RF) transmission line and,'more particularly, to such a DC conductive connection which spans the air filled space separating the condoctors, and which has substantially no effect on the RF transmission characteristic of the transmission line.

As fully described in my copending application, a DC connection to the center conductor of a coaxialline is provided by a fine wire coil compression spring which is axially supported along its length by a radial bore in the solid dielectric spacer separating the conductors. This spring is compression-loaded between the center conductor and either the outer conductor or an electrical contact outside the outer conductor and insulated there- 'i from to provide a DCconnection therebetween. The coils,

because of their inductive impedance at the RF frequencies, provide an RF open circuit.

The compression-loaded spring connection between the conductors of a transmission line (or between one conductor of a transmission line and some other electrical contact pad usually in the plane or just outside the other conductor of the transmission line) described in my copending application relies on a bore in the solid dielectric spacing material for axially supporting the spring along its length across the space between the conductors. However, there are RF transmission lines in which the space between the conductors is not entirely filled with a solid dielectric and where it is either desirable or necessary to make a DC connection across an unfilled space. In such cases other means have to be provided to support the spring along its length. This is particularly true for some striplines in which the conductive strip is only supported upon the ground plane from below and the remaining enclosure provides only air space separation. In such a transmission line structure a DC connection from above requires support means. There are also transmission line structures which are formed by metallizing an alumina oxide ceramic substrate, known as microstrip transmission lines, in which a bore in the ceramic which would not only be hard to fabricate, but the strip, being formed by thin film techniques, would be unable to support the 3,521,202 Patented July 21, 1970 spring. In this case the connection must be made to the strip from the side opposite the substrate.

It is therefore a primary object of the present invention to provide a DC connection to the conductor of an RF transmission line across an air filled space which does not materially affect the RF transmission characteristics of the line.

It is a further object of the present invention to provide a compression-loaded spring connection to one of the conductors of an RF transmission line across the air space separating the line conductors.

It is also an object of the present invention to provide a DC connection to the strip conductor of a strip transmission line structure which has substantially no effect on the lines RF properties.

SUMMARY OF THE INVENTION The present invention utilizes a fine wire coil compression spring, either loosely fitted about an insulator core or loosely fitted into an insulator sleeve, for forming a compression-loaded DC connection to at least one conductor of an RF transmission line which extends across the air space separating the conductors. The core or sleeve assure that the spring retains axial integrity along its length and makes good compression contacts with the conductors at its ends.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a segmented perspective view of a stripline portion showing a core supported compression spring making contact with the strip; and

FIG. 2 is a view, similar to the one shown in FIG. 1 of a microstripline portion Within an envelope showing a sleeve supported compression strip making contact with the strip.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, and particularly to FIG. 1 thereof, there is shown a typical strip transmission line 10 comprising a strip conductor 12 supported upon a ground plane 14 by a solid dielectric spacer support 16. As is usual in striplines, a conductive box or envelope or second ground plane 18, in electrical contact with ground plane 14, such as by "lead 15, is provided and dimensioned for obtaining the desired characteristic line impedance and for suppressing undesirable modes.

It should be noted at this point that there exists a choice of making a DC connection to strip 12, namely, the connection may be made across the air space from above or across the solid dielectric from below. While it is possible to provide a cylindrical bore in solid dielectric spacer 16, extending from ground plane 14 to strip 12, for accommodating and supporting a compression-loaded spring, the embodiment shown in FIG. 1 shows a DC connection across the air space above conductive strip 12. Such a placement of the compression-loaded spring is particularly important where the striplines are formed by thin film metallizing of an alumina oxide ceramic substrate (see FIG. 2) in which a cylindrical bore would be difficult to provide and in which the conductive film would be unsuitable for supporting the ends of a compression-loaded spring.

As shown in FIG. 1, a coil compression spring 20, constructed of a conductive spring material such as stainless steel wire and having a free length (uncompressed) which is greater than the width of the gap it is to span, is compression-loaded between strip 12 and a support plate 24. Spring 20 is axially supported along its length by a solid dielectric core member 22 which may be rigidly attached to support plate 24 as shown, or which may be unattached and loosely contained in spring 20.

In the event that electrical isolation between strip 12 and ground plane 14 is desired, support plate 24 is constructed either of an insulating material or, if metallic, is provided with an anodized lower surface. In that case, also, plate 24 may be provided with a conductive annular ring 26 which overlies a circular aperture 28 in envelope 1% through which spring 20 is inserted into the interior of line 10. The center of ring 26 may be dimensioned to hold core 22. Electrical contact to spring 20 is made by attachment of suitable leads (not shown) to annular ring 26. In the case that an electrical connection to enve'lope 18 is desired, plate 24 is conductively affixed to the envelope.

Referring now to FIG. 2, there is shown a transmission line structure 30 having a microstripline 32 housed within an envelope 34 dimensioned to provide the desired characteristic impedance and mode suppression. Microstripline 32 comprises an alumina oxide ceramic substrate 36 having a film strip 38 and a film ground plane 40, both films being formed by metallizing using thin film or thick film methods.

A DC connection across the upper air space between envelope 34 and strip 38 is established by a compressionloaded spring 42 which is inserted into the space through an aperture 44 in envelope 34 which is dimensioned to also allow the insertion of a sleeve 46 made of an insulating material.

Sleeve 46 may either be loosely fitted about spring 42 as shown, or may be attached to a support plate 48. Its sole function, as that of core 20, is to prevent spring 42 from buckling along its length and thereby lose its pressure cont-act, at opposite ends, with the strip and the other contact. In case strip 38 is to be insulated from envelope 34 (ground plane 40), support plate 48 may be constructed of an insulator and have a contact plug overlying spring 46, or else it may be metallic with an insulating surface between it and envelope 34.

In selecting the physical configuration of the spring, it is desirable, as fully explained in my referenced copending application, to have a maximum number of turns and a maximum coil diameter so that the inductive impedance is a maximum and the presence of the spring has a negligible elfect on the RF energy transmitted through the transmission line. To obtain the largest number of turns, the fully compressed length of spring 20 is made slightly smaller than the gap distance between strip 12 and the inner surface of cover plate 24. The reason the fully compressed length is made slightly smaller is to prevent adjacent coils from touching. Further, the diameter of the coil itself, which also determines the maximum number of turns of the spring, is held to a minimum commensurate with the desired current carrying and spring force requirements. The outside coil diameter is selected as large as possible, but it has been found that the diameter need not be larger than the width of the center strip for good RF isolation and, in fact, may be considerably smaller.

There has been described a DC connector for use in a stripline which is mechanically rugged, economical to install, and provides excellent DC conduction and RF isolation.

What is claimed is:

1. A direct current conductive connection across an air gap between one of the conductors of an RF transmission line and a further conductor, which has negligible eflFect on the transmission lines RF properties, said conductive connection comprising:

an axially elongated, conductive coil spring compression-loaded between the transmission line conductor and the further conductor to establish good conductive pressure contacts between opposite ends of said spring, the transmission line conductor and the further conductor, respectively; and

a solid dielectric spring support member within said air gap and associated solely with said coil spring to constrain said coil spring along its length in an axial direction.

2. A direct current conductive connection in accordance with claim 1 in which said further conductor is the other conductor of the transmission line.

3. A direct current conductive connection in accordance with claim 1 in which said support member is formed by an elongated core disposed within said coil spring.

4. A direct current conductive connection in accordance with claim 1 in which said support member is formed by a substantially cylindrical sleeve disposed in surrounding relation to said coil spring.

5. A direct current conductive connection in accordance with claim 1 in which said further conductor is formed by a plate-like member and in which said support member is formed by an elongated core disposed within said coil spring and in which said core is carried by said plate-like member.

6. A direct current conductive connection in accordance with claim 1 in which said further conductor is formed by a plate-like member and in which said support member is formed by a substantially cylindrical sleeve disposed in surrounding relationship to said coil spring and in which said sleeve is carried by said platelike member.

References Cited UNITED STATES PATENTS 3,423,702 1/1969 Russel 333-97 HERMAN KARL SAALBACH, Primary Examiner M. NUSSBAUM, Assistant Examiner US. Cl. X.R. 333; 33620 

